The invention relates to a method and an apparatus for separating wood products, particularly chips and composite fiber materials, used furniture, automobile composite materials, etc., into reusable individual components, such as chips and fiber bundles, fibers, granulates, powders and the like. The method according to the invention and the associated apparatus are intended to extensively maintain the slenderness ratio (the ratio of length to diameter) of the chips, fiber bundles and fibers without perceptible shortening. The slenderness ratio is a significant prerequisite for high stability values and a well-closed surface of new materials and composite materials produced from the old ones.
Numerous methods for recycling the aforementioned materials are known. They represent solutions that are cost-effective to some extent, but have a considerable negative impact on the slenderness ratio. The methods range to granulating the materials, which typically results in a low-quality recycled product. Other methods are suitable for maintaining a high slenderness ratio, but are cost- and labor-intensive. These methods also have a limited throughput, which also negatively influences the associated costs. There are still no suitable reprocessing methods for some used products, however, which leaves only thermal disposal.
The simplest solution, albeit one that has a strong negative impact on the slenderness ratio, is to mechanically comminute the aforementioned materials in a shredder or a hammermill. Shredders can have a single- or two-stage design. Shredders are modified hammermills having a horizontal or vertical intake and tools of various shapes, with or without a grinding track as a counterpart to the hammer mechanism, and with or without the stationary screen or grate part that surrounds the grinding space. The product generated with this system tends to possess the quality of a granulate or filler.
The quality of wood products that are re-processed with the above-described shredder systems can be greatly improved if the feed material is wetted in order to reduce its brittleness. This measure results in fewer small particles and less breakage transversely to the fiber axis. Shredders, hammermills and similar machines are, however, relatively sensitive to moisture. The throughput decreases progressively as the humidity level rises. Jamming begins to occur when the material is between 30 and 40% absolutely dry. For polymer-containing composite materials, moistening and jamming are usually not issues, because these materials can absorb little or no moisture.
Much better results are attained, at least with wood products, when, in accordance with DE 195 09 152, the aforementioned materials are pre-comminuted to have edge lengths of 10-20 cm, then impregnated with a saturating and impregnating solution and, finally, subjected to a steam temperature of 80 to 100 degrees Cxc2x0 in an autoclave for a lengthy reaction time. The impregnating solutions used here are formulated to exert a hydrolyzing effect on the glued joints, so the chips of a particle board, for example, separate from one another due to the hydrolyzing of the glued joints, on the one hand, and the pressure caused by swelling, on the other hand. They can subsequently be separated from one another through screens or the like, and fractionated. The result is a superior recycled chip with an extensively non-reduced slenderness ratio.
The method is relatively costly, however. It requires hydrolyzing chemicals. To accelerate the penetration of these chemicals into the pre-comminuted material, a vacuum must be created in a pressure tank. Finally, steam must be introduced into the pressure tank at a pressure of up to two bar.
The output of this batch-wise operation is low; a comparison of the total investment and the operating costs to the throughput reveals that the product is very good, but the costs are too high.
AS 1 201 045 is analogous in some ways to DE 195 09 152. Here, however, no chemicals are used; instead, a steam pressure of up to five bar is applied. After a reaction time of several hours, chip materials break down into individual components and can be separated from one another through screening.
EP 0 581 039 discloses a further method, which likewise operates on the basis of steam decomposition. Board-type elements and used furniture with or without laminates are broken down into large pieces so they can fit into the pressure chamber of an autoclave. Then, the autoclave is filled with steam in a temperature range between 120 and 180xc2x0. At the same time, binding agents that can be hydrolyzed are hydrolyzed, and the chips swell, resulting in the dissolution of the particle-board composite. In contrast to the above-cited publications, in this case, the chip material is subsequently cleaned with a cleaning fluid of hydrolysis products. The necessity of using chemicals that promote hydrolysis, or cleaning fluids, but especially the necessity of using an autoclave with steam in a pressure range between two and five bar, makes the above-described methods costly.
It is the object of the present invention to provide a method and the associated, necessary production system for obtaining a recycled product, the product having good slenderness ratios, at low cost and with a purely mechanical, continuous production procedure that does not employ chemicals, an autoclave, cleaning fluid or live steam. Above all, the method and apparatus according to the invention are intended to be applicable not only to wood products and used furniture, but also to materials and composite materials with high polymer and duromer contents, which cannot be brought into a state in which they can be more easily broken down with the application of moisture.